Well, It looks like we can change the displayed name - You will still logon as the original user account ID, in this case, plyonsTEST1, but what is displayed is the new name. e.g., plyonsTEST2.

To change the displayed name, go to your profile settings. Select the hyperlink to modify your account related settings. Change the dispayed name. The account name / logon ID will STAY THE SAME. But what everyone sees will be the NEW name.

Your number of posts remains the same as your logon ID does not change - just the display name changes.. IF you change your logon account ID instead, e.g., delete old account, create new account, then you are correct, you will lose your seniority.